Correct Answer:
C. Sound file
File extensions are crucial identifiers that tell an operating system and applications what type of data a file contains and how to process it. In the context of PowerPoint, various file types can be inserted to enrich a presentation. A .wav file (Waveform Audio File Format) is a widely recognized standard for storing uncompressed digital audio. It is a common format for high-quality sound recordings and is readily supported for insertion into PowerPoint presentations. Therefore, a .wav file is unequivocally a type of Sound file. It is not a video file (e.g., .mp4), an image file (e.g., .jpg), or a presentation file itself (e.g., .pptx).